The long term objectives and specific aims are 1) to determine the precise innervational patterns in several different types of reptilian auditory papillae; 2) to systematically describe the fine structure of the sensory and supporting cells of both the auditory papillae and the vestibular maculae and cristae; 3) to define and describe the normal cycle of events and to determine the stimulating factors in the phenomenon of "hypersynaptogensis" found in adult auditory hair cells, and 4) to describe the ontogeny of synaptogenesis of the auditory and vestibular organs in a lizard, Xantusia vigilis. Precise patterns of innervation are determined by serial transmission electron micrography followed by three dimensional reconstruction. The innervational details will be described in two types of primitive papillae, and two types of specialized papillae. The auditory and vestibular organs of a considerable variety of reptiles has already been collected, fixed, and plastic embedded. This material will provide the material for study of the fine structure of these organs. The phenomenon of adult synaptogenesis will be studied by collecting animals at monthly intervals throughout the yearly cycle and correlating changes in synaptogenic activity with light, heat, and the reproductive phase of the life cycle. Experimental alteration of this phenomenon will also be attempted. The information gained from the above studies will be of great value in the understanding of auditory function in man and other vertebrate animals. The fine structure of the auditory papillae and vestibular maculae and cristae from a large variety of previously collected reptile and plastic embedded tissues will be studied.